1. Field of the Invention
The present invention relates to position measurement methods, position control methods, measurement methods, loading methods, exposure methods and exposure apparatus, and device manufacturing methods, and more particularly to a position measurement method in which position information of a plate mounted freely detachable on a moving body is measured; a position control method that uses the position measurement method, a measurement method in which information related to a plate where an opening is formed in order to mount an object is measured, a loading method that uses the measurement method, an exposure method that utilizes the loading method and an exposure apparatus suitable for performing each of the methods described above, and a device manufacturing method that uses the exposure apparatus or the exposure method.
2. Description of the Related Art
Conventionally, in a lithography process for manufacturing electronic devices such as a semiconductor device (an integrated circuit or the like), a liquid crystal display device, or the like, a reduction projection exposure apparatus (the so-called stepper) by the step-and-repeat method that transfers a pattern formed on a mask or a reticle (hereinafter generally referred to as a ‘reticle’) onto a photosensitive object such as a wafer or a glass plate (hereinafter generally referred to as a ‘wafer’) on which a resist (a photosensitive agent) is coated, or a projection exposure apparatus (the so-called scanning stepper) by the step-and-scan method is mainly used.
Due to higher integration and finer circuit patterns of the semiconductor devices, in order to improve the resolution of the projection optical system equipped in the projection exposure apparatus, the wavelength of the exposure light (exposure wavelength) is becoming shorter while the numerical aperture (NA) of the projection optical system is gradually increasing. Meanwhile, depth of focus is becoming smaller, due to such shorter exposure wavelength and increasing numerical aperture (larger NA). The exposure wavelength is presumed to be shorter in the future, and if such a situation continues, the depth of focus may become so small that margin shortage may occur during the exposure operation.
Therefore, as a method of substantially shortening the exposure wavelength while increasing (widening) the depth of focus when compared with the depth of focus in the air, the exposure apparatus that utilizes the immersion exposure method is beginning to gather attention. As the exposure apparatus that utilizes the immersion method, an exposure apparatus that performs exposure in a state where the space between the lower surface of the projection optical system and the wafer surface is locally filled with liquid such as water or an organic solvent is known (refer to, for example, the pamphlet of International Publication No. WO99/49504). In the exposure apparatus according to the pamphlet, the resolution is improved utilizing the fact that the wavelength of the exposure light in the liquid becomes 1/n of the wavelength in the air (n is the refractive index of the liquid which is normally around 1.2 to 1.6), and also the depth of focus is substantially increased n times when compared with the case where the same resolution is obtained by a projection optical system (supposing that such a projection optical system can be made) that does not employ the immersion method. That is, the depth of focus can be substantially increased n times than in the air.
Recently, in wafer stages of the exposure apparatus, a proposal has been made of disposing a freely detachable plate that forms a flat section substantially flush with the wafer in the periphery of the wafer held by the wafer stage. In the case of using such a detachable plate in the wafer stage, the position of the plate has to be precisely known.
In addition, in the case of using such plate in the wafer stage, an opening (such as an opening with a circular shape in the case of a semiconductor wafer) for positioning the wafer has to be formed in the center of the plate. However, for example, in the case the degree of roundness of the circular opening of the plate is low and the circular shape is deformed or in an ellipse, the gap between the circumferential surface of the wafer and the inner circumference surface of the opening becomes uneven, and inconveniences could occur, such as the wafer coming into contact with the inner wall surface of the opening of the plate, or not being able to insert the wafer into the opening of the plate.
In addition, because the gap between the inner wall surface of the opening of the plate and the wafer is extremely small, smooth loading operation of the wafer will be difficult if the relative position of the wafer and the plate is not accurately aligned when loading the wafer.
In addition, in the case of the exposure apparatus that utilizes the immersion method, there was the risk of the liquid flowing into parts where the gap between the inner circumference edge of the opening of the plate and the outer circumferential edge of the wafer is large.